1. Field of the Invention
The present invention relates to a substrate comprising a three element alloy, and particularly, relates to a substrate wherein the three element alloy comprising the Au/Ag/grain element is applied to a nickel layer which is applied to the copper or copper alloy, or nickel or nickel alloy, to provide the desired characteristics of improved bondability, corrosion durability, adhesion to mold resin and cost effectiveness.
2. Background Art
Generally, the substrates for a semiconductor device make electrical interconnections between electrical and electronic devices, which includes such devices as a semiconductor chip and a printed circuit board (xe2x80x9cPCBxe2x80x9d). Moreover, the characteristics of a good substrate material include bondability to connecting wires, durability from corrosion, adhesion to the mold resin (which typically acts as a cover), and ductility for manipulation.
To achieve such characteristics, conventional substrates for a semiconductor device have used an outermost layer of Snxe2x80x94Pb in a multi-plated layer structure also including a copper layer and nickel layer, However, lead is widely considered to be a health hazard. Lead is toxic to human individuals and it has a long documented history of adverse impact on humans and the environment.
Conventionally, alternatives to the Snxe2x80x94Pb layer have been a palladium layer or a gold layer as the outermost layer. However, a palladium layer or a gold layer has manifest problems in wire bondability, adhesion to the mold resin, and attachment characteristics for a PCB. Additionally, the costs of using palladium and of gold have traditionally been fairly high.
An object of the present invention is to provide substrates that are lead-free and thus environmentally friendly, while at the same time, providing the desired characteristics of improved bondability, corrosion durability, adhesion to mold resin, and cost effectiveness.
To achieve this object, the present invention uses the three element alloy comprising gold, silver and grain element selected from selenium, antimony, bismuth, nickel, cobalt and indium.